Topic: First Boat, Several Questions <br />EQCM2B<br />New Member <br />Posts: 2<br />From:<br />Registered: Jul 2001 <br /> posted July 29, 2001 01:23 AM <br />--------------------------------------------------------------------------------<br />Recently bought 1973 15ft DUO Sportster with 50hp Evinrude on it. The motor seems to run ok but the max speed that I have reached is about 25mph. The tach does work and I want to say that the max RPM attained was about 3500 while under a load. The prop is a 13-3/4 x15. If I try to pull a tube I might get 10 mph out of it. This was done with 2 people in the boat and one in the tube.<br />I would also like to know the year if possible. The serial # is 07812 and the model # is 50173s. <br /><br />I would like to know am I expecting to much from a 50 hp engine or do I have a little work to do to give me what I would like.<br /><br />IP: Logged<br /> <br />Navigator<br />Member <br />Posts: 86<br />From:Tampa, FL, USA<br />Registered: Feb 2001 <br /> posted July 30, 2001 09:53 AM <br />--------------------------------------------------------------------------------<br />EQCM2B<br />First off, welcome to the board!<br />Your problem is that you are "Over Propped", that is, you're prop has too much pitch and you're engine is killing itself. If the engine cant reach normal operating range, you will lug the engine and cause high carbon buildup which eventually make the powerhead fail.<br /><br />You're current prop is a 13.75x15. What you want to do is decrease the pitch of your prop until your boat (When normally loaded)operates in the middle to high end of the engines mfgr's recommended operating range.<br /><br />A 1 inch decrease in pitch will yield roughly a 200 rpm increase in rpms. The 3500 rpm you mentioned, was that regular cruising or while pulling a tube? <br /><br /><br />Check what your engines normal operating range should be, then do the math for the correct size prop. (I dont know the range for your engine otherwise I'd tell you, sorry, It's probably 4500-5500 I'd guess). I would guess an 11" or 12" pitch prop is what you'll need. What you dont want to do, is get too low a pitch that allows the engine to exceed the range.<br /><br />Anyways, with the correct size prop, your boat should be able to cruise faster and pull the tuber out of the water without all the strain.<br /><br />Nav <br /><br /><br />IP: Logged<br /> <br />Hey its Me_Fone_man<br />Member <br />Posts: 31<br />From:Franklin, TN<br />Registered: Jul 2001 <br /> posted July 30, 2001 10:01 AM <br />--------------------------------------------------------------------------------<br />"I would also like to know the year if possible. The serial # is 07812 and the model # is 50173s."<br />---------------------------------------------<br />Model: 50173S<br />Serial #: 07812<br />Year: 1971<br />HP: 50 Hp<br /><br /><br />------------------<br />"Keep it between the Bouys & Good Luck"<br /><br />fone_man<br /><br />IP: Logged<br /> <br />Hey its Me_Fone_man<br />Member <br />Posts: 31<br />From:Franklin, TN<br />Registered: Jul 2001 <br /> posted July 30, 2001 10:03 AM <br />--------------------------------------------------------------------------------<br />Also, I would assume new to iboats... you will get a quicker answer to your "engine-motor" needs on that side of board.<br />Just copy the whole thing over to that side.<br /><br /><br />------------------<br />"Keep it between the Bouys & Good Luck"<br /><br />fone_man<br /><br />IP: Logged<br /> <br />EQCM2B<br />New Member <br />Posts: 2<br />From:<br />Registered: Jul 2001 <br /> posted July 31, 2001 09:32 AM <br />--------------------------------------------------------------------------------<br />Thanks for the help. The 3500 RPM was without pulling a tube. Do I need to change the size from 13.75 down to an 11 or 12 also or will just a change in pitch give me what I need?<br />IP: Logged
